Some combustion engines require spark plugs to provide an ignition source for igniting air/fuel mixture residing within each cylinder. A spark plug may be threaded into the cylinder head of the engine, thereby locating a spark gap of the spark plug within an engine cylinder. The spark gap is defined by a space between the anode and the cathode of the spark plug. The cathode is normally grounded to the engine through the spark plug threads connecting the spark plug to the engine.
The spark plug anode is in electrical communication with an electric potential source, usually through an axial conductor. The axial conductor extends from the spark plug anode, through the spark plug, to an outer terminal contact. The outer terminal contact is usually in electrical communication with the electric potential source through a wire connected therebetween. An electric arc may be established across the spark gap when a sufficient electric potential is applied across the spark gap. In turn, the electric arc may provide sufficient ignition energy to ignite a fuel fuel-air mixture residing within the corresponding engine cylinder.
Many spark plugs include an axial conductor enclosed within a ceramic insulator, an outer terminal contact disposed at an end of the spark plug disposed outside the engine, a center electrode, a lower end contact terminal containing the tip of the spark plug and the spark gap, and a threaded cylindrical body that surrounds at least a middle portion of the spark plug and enables the plug to be threaded into the cylinder head.
Some spark plugs have well-documented histories of being difficult to remove from the cylinder heads of certain engines. At least one vehicle manufacturer incorporates a certain spark plug design which has proven difficult to remove from the cylinder head without breaking. The issue exists in some Ford Motor Company vehicles, as particularly described in Technical Service Bulletins TSB 06-15-2 and TSB 08-7-6. During removal of such spark plugs, the cylindrical tip may break and separate from the body of the threaded plug. The broken tip remains within the cylinder head and must be removed before a new plug can be threaded into the cylinder head.
Others have recognized difficulty of removing the Ford spark plugs from engines, and have proposed tools that use drills and taps to assist in the removal of the broken tips. After drilling and tapping threads into the broken spark plug tip, such tools are screwed into the plug tip, and both the tool and the tip are then pulled from the cylinder head together. However, the process of drilling and tapping the broken spark plug tip is both difficult and time consuming, at least in part because of the difficulties of aligning the drilling and tapping operations with the broken spark plug tip.
Thus, there exists a need for new apparatus and methods for extracting spark plugs from engines to address the problems discussed above.